allow specifying an ios version for the llvm target

Author: ubamrein

compiler/rustc_target/src/spec/apple_base.rs

@@ -92,6 +92,12 @@ fn ios_deployment_target() -> (u32, u32) {
 }
 
 pub fn ios_llvm_target(arch: &str) -> String {
+    // Modern iOS tooling extracts information about deployment target
+    // from LC_BUILD_VERSION. This load command will only be emitted when
+    // we build with a version specific `llvm_target`, with the version
+    // set high enough. Luckily one LC_BUILD_VERSION is enough, for Xcode
+    // to pick it up (since std and core are still built with the fallback
+    // of version 7.0 and hence emit the old LC_IPHONE_MIN_VERSION).
     let (major, minor) = ios_deployment_target();
     format!("{}-apple-ios{}.{}.0", arch, major, minor)
 }

compiler/rustc_target/src/spec/armv7_apple_ios.rs

@@ -3,7 +3,7 @@ use crate::spec::{Target, TargetOptions};
 
 pub fn target() -> Target {
     Target {
-        llvm_target: "armv7-apple-ios".to_string(),
+        llvm_target: super::apple_base::ios_llvm_target("armv7"),
         pointer_width: 32,
         data_layout: "e-m:o-p:32:32-Fi8-f64:32:64-v64:32:64-v128:32:128-a:0:32-n32-S32".to_string(),
         arch: "arm".to_string(),

compiler/rustc_target/src/spec/i386_apple_ios.rs

@@ -4,7 +4,7 @@ use crate::spec::{StackProbeType, Target, TargetOptions};
 pub fn target() -> Target {
     let base = opts("ios", Arch::I386);
     Target {
-        llvm_target: "i386-apple-ios".to_string(),
+        llvm_target: super::apple_base::ios_sim_llvm_target("i386"),
         pointer_width: 32,
         data_layout: "e-m:o-p:32:32-p270:32:32-p271:32:32-p272:64:64-\
             f64:32:64-f80:128-n8:16:32-S128"

compiler/rustc_target/src/spec/x86_64_apple_ios.rs

@@ -4,7 +4,7 @@ use crate::spec::{StackProbeType, Target, TargetOptions};
 pub fn target() -> Target {
     let base = opts("ios", Arch::X86_64);
     Target {
-        llvm_target: "x86_64-apple-ios".to_string(),
+        llvm_target: super::apple_base::ios_sim_llvm_target("x86_64"),
         pointer_width: 64,
         data_layout: "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128"
             .to_string(),